1. Field of the Invention
The present invention relates to an electronic circuit device able to carry out a diagnosis of status-holding circuits in the electronic circuit device by scanning. Usually, in the diagnosis of status-holding circuits in an electronic circuit device, a scanning is carried out to read data from status-holding circuits such as latch circuits, flip-flop circuits, and the like, or to write data into these status-holding circuits.
2. Description of the Related Arts
In general, in the diagnosis of status-holding circuits in an electronic circuit device, a parallel scanning method in which a scan address is supplied in parallel to a plurality of address signal lines corresponding to the number of bits of a scan address, and a serial scanning method in which a scan address is supplied successively through a signal line to a serial-parallel converter and converted into a parallel scan address and then fed to a status-holding circuit, are used.
However, in the parallel scanning method, when a large number of status-holding circuits must be scanned, a large number of address signal lines must be provided for supplying scan addresses; which increased number of address signal lines is disadvantageous.
In the serial scanning method, a large amount of hardware is needed for the serial-parallel conversion of scan addresses, and such an increased amount of hardware is also disadvantageous.